Humboldt Bay is a natural bay and a multi-basin, bar-built coastal lagoon located on the rugged North Coast of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

, entirely within Humboldt County, United States. It is the largest protected

body of water A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such a ...

on the West Coast between

San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water f ...

and

Puget Sound Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected m ...

, the second-largest enclosed bay in California, and the largest port between San Francisco and

Coos Bay Coos Bay is an estuary where the Coos River enters the Pacific Ocean, the estuary is approximately 12 miles long and up to two miles wide. It is the largest estuary completely within Oregon state lines. The Coos Bay watershed covers an area of abou ...

Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...

. The largest city adjoining the bay is

Eureka Eureka (often abbreviated as E!, or Σ!) is an intergovernmental organisation for research and development funding and coordination. Eureka is an open platform for international cooperation in innovation. Organisations and companies applying th ...

, the regional center and county seat of Humboldt County, followed by the city of

Arcata Arcata (; Wiyot: ''Goudi’ni''; Yurok: ''Oket'oh'') is a city adjacent to the Arcata Bay (northern) portion of Humboldt Bay in Humboldt County, California, United States. At the 2020 census, Arcata's population was 18,857. Arcata was first ...

. These primary cities, together with adjoining unincorporated communities and several small towns, comprise a Humboldt Bay Area with a total population of nearly 80,000 people. This comprises nearly 60% of the population of Humboldt County. The bay is home to more than 100 plant species, 300 invertebrate species, 100 fish species, and 200 bird species. In addition, the bay and its complex system of marshes and grasses support hundreds of thousands of migrating and local shore birds. Commercially, this second-largest

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

in California is the site of the largest oyster production operations on the West Coast, producing more than half of all

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...

s farmed in California. The Port of Humboldt Bay (also referred to as the Port of Eureka) is a deep water port with

harbor A harbor (American English), harbour (British English; see spelling differences), or haven is a sheltered body of water where ships, boats, and barges can be docked. The term ''harbor'' is often used interchangeably with ''port'', which is a ...

facilities, including large industrial docks at Fairhaven,

Samoa Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands ( Savai'i and Upolu); two smaller, inhabited islands ( Manono and Apolima); ...

, and Fields Landing designed to serve cargo and other vessels. Several marinas also located in Greater Eureka have the capacity to serve hundreds of small to mid-size boats and pleasure craft. Beginning in the 1850s, the bay was used extensively to export logs and

forest products A forest product is any material derived from forestry for direct consumption or commercial use, such as lumber, paper, or fodder for livestock. Wood, by far the dominant product of forests, is used for many purposes, such as wood fuel (e.g. in f ...

as part of the historic West coast lumber trade, but with the decline of the industry lumber now is only infrequently shipped from the port.

Geography

Humboldt Bay is the only deep water bay between the

and

. The Port of Humboldt Bay is the only protected deep water port for large ocean-going vessels for the large region. Despite being the only protected harbor along nearly of coastline, the bay's location was undiscovered or at least unreliably charted for centuries after the first arrival of European explorers to the Pacific Coast. This is partially because the bay is difficult to see from the ocean. The harbor opens to the sea through a narrow and historically treacherous passage, which was blocked from direct view because of sandbars. Formation of such sandbars is now managed by a system of jetties. Contributing to the bay's isolation were features of the coastal mountain range, which extends from the ocean approximately inland, and the common marine layer (fog) in addition to frequent clouds or rain. The bay is approximately long but can be from wide at the entrance to the widest point at in the North Bay. The surface area of Humboldt Bay is of which are intertidal mudflats. More than are primarily eelgrass habitat, which has been relatively constant since 1871, although more than 80% of the bay's coastal marsh habitats have been lost or fragmented by

levee A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...

railroad Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a prep ...

and

highway A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In some areas of the United States, it is used as an equivalent term to controlled-access ...

construction. At high tide the surface area is approximately , but it is at low tide. Each tidal cycle replaces 41% of the water in Humboldt Bay, although exchange in small channels and sloughs of the bay can take up to three weeks.

Geomorphology

Humboldt Bay began to form when a river valley drowned about 10,000 to 15,000 years ago during a period of rapid sea level rise. Bay sediments also contain buried salt marsh deposits showing that areas of the bay have subsided during episodic large-magnitude

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, fr ...

s. Three rivers, the Mad, Elk, and Eel, drained into Humboldt Bay during the mid-

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

. Subsequently, the Mad River cut a new outlet to the sea, and the flow of the Eel was diverted by

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal th ...

of Table Bluff at the southern end of the bay, but Elk River continues to drain into Humboldt Bay. In the 21st century, the bay is considered to have three regions: * the North Bay to the north of

Bridge * the Entrance Bay from Samoa Bridge to South Jetty * the South Bay, which is the remainder of the bay to the south Daby, Woodley, and Indian islands are in the North Bay, and all three are within the City of Eureka. Low tides reveal two more islands: Sand Island, which was formed from

dredge Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing da ...

spoils left in the early 20th century, and Bird Island. A large

eelgrass Eelgrass is a common name for several plants and may refer to: * ''Zostera'', marine eelgrass * ''Vallisneria'', freshwater eelgrass {{Short pages monitor